<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" @click="handleLetterClick" @touchstart="handleTouchstart" @touchmove="handleTouchMove" @touchend="handleTouchEnd" :ref="item">{{item}}</li>

    </ul>
</template>
<script>
export default {
  name: "CityAlphabet",
  props: {
    cities: Object
  },
  computed: {
    letters() {
      let letters = [];
      for (let item in this.cities) {
        letters.push(item);
      }
      return letters;
    }
  },
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    };
  },
  updated() {
    this.offsetTopstartY = this.$refs["A"][0].offsetTop;
  },
  methods: {
    handleLetterClick(e) {
      this.$emit("change", e.target.innerText);
    },
    handleTouchstart() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer);
        }
        this.timer = setTimeout(() => {
          const moveY = e.touches[0].clientY - 79;
          const index = Math.floor((moveY - this.startY) / 20);
          if (index >= 0 && index < this.letters.length) {
            this.$emit("change", this.letters[index]);
          }
        }, 16);
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
};
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl';

.list {
    display: flex;
    justify-content: center;
    flex-direction: column;
    position: absolute;
    right: 0;
    top: 1.58rem;
    bottom: 0;
    width: 0.4rem;

    .item {
        color: $bgColor;
        text-align: center;
        line-height: 0.44rem;
    }
}
</style>
